A continuous growth in network traffic drives a single-channel bit rate in a wavelength division multiplexing system to gradually develop from 10 gigabits per second (10 G) over ten years ago to 40 G and 100 G; and even to 4006 and 1 terabyte per second (IT) in the future. For a network system in which a single-channel rate is below 1000 a conventional spectrum interval of 50 gigahertz (GHz) can meet a requirement. However, when the bit rate reaches 400 G, 1 T, and even higher, a spectral width occupied by a signal will exceed 50 GHz. Therefore, on an existing network, when a signal with a rate of 400 G or above is borne, a high-rate signal needs to be divided into multiple low-rate signals. For example, a 400 G signal is divided into four 100 G signals, and each 100 G signal is borne by using a fixed frequency band of 50 GHz. This is feasible regarding network implementation, but inevitably causes a decrease in spectrum utilization in comparison with a continuous 400 G signal.
Therefore, to improve network spectrum resource utilization, a new network emerges—a “flexible bandwidth optical network”. Bandwidth occupied by different signals is no longer limited to 50 GHz or an integer multiple of 50 GHz, but exists in a form of a flexible interval (Flexgrid). A change in a network structure inevitably requires adaptation of various optical components to the change. The optical components include a core switch component, that is, a wavelength selective switch (WSS). An early WSS is mainly an optical engine based on a micro-electro-mechanical system. However, there is a particular gap between various micromirrors in the micro-electro-mechanical system. Therefore, when multiple micromirrors are required for implementing a wide-spectrum filter, some grooves are generated between spectra. As a result, a spectral width of the filter cannot meet a “Flexgrid” requirement. In view of this, a new optical engine based on liquid crystal on silicon (LOS) is provided in the industry. The LCOS can implement a “Flexgrid” filter function, and therefore gradually becomes a mainstream technology.
An operating principle of the LCOS lies in that different voltages are loaded on different pixels of the LCOS. Because of a birefringent effect of liquid crystal, the different voltages correspond to different phase delays, thereby forming a structure similar to a blazed grating. A diffraction angle of the blazed grating depends on a grating period of the blazed grating. Therefore, a diffraction angle of incident light may be controlled merely by changing grating periods corresponding to different positions on the LCOS. This allows diffractive light to be output at different ports of the WSS, implementing a WSS function. Because there are millions of pixels on the LCOS and a gap between the pixels is very small, the Flexgrid filter function can be implemented very flexibly, and in addition, there is no spectrum gap.
However, because the operating principle of the LCOS is based on a diffraction effect, when diffractive light required by us is obtained, light at high diffraction orders is also generated due to a phase error. As shown in FIG. 1, FIG. 1 is a schematic structural diagram of a WSS. FIG. 1 is a schematic diagram for describing a crosstalk generation cause, and does not show a complete structure of the WSS. In FIG. 1, light entering an input port undergoes a series of processing (which may include deflection processing, demultiplexing and multiplexing processing, and the like) in the black box, and then is incident on an LCOS panel. A corresponding pixel on the LCOS diffracts required +1-order diffractive light to a corresponding output port according to a corresponding configuration. However, in this case, light at other diffraction orders may possibly enter other output ports. After entering a corresponding input port, diffractive light such as 0-order, −1-order, and +2-order diffractive light may possibly cause crosstalk on an optical link subsequently. For example, in FIG. 1, when the +1-order diffractive light needs to be output from output port 3, light at other diffraction orders may be possibly output from other ports as crosstalk light, causing intra-frequency crosstalk. However, once entering the corresponding output ports, this part of signals are difficult to eliminate, affecting system performance. Therefore, to improve the system performance of the LCOS-based WSS, a solution needs to be found to effectively suppress crosstalk signals.